How do I add (a chrome) texture without a 2D image? "TxDiffuse missing" error
If you're exporting your material outside of Blender, the node setup you used to create the material will no longer work. It's like the node setup is a dynamic material and to export it you need to save a still version of it (i.e. bake it).
There's a really good explanation of how to do that here: How do I bake a texture using Cycles bake
In essence, you choose a look you like and create a texture (a still image) for the object's surface. When you export that object into whatever other program you're using, you apply that texture (image) as its material, and you get the same look you had when you baked the material. The UV map is what is used to assign the right parts of the texture you made to the right parts of the object. Of course, that means the material isn't dynamic anymore, so you can either deal with that or combine the texture with whatever builtin material editor the program you're using has.
For a metallic material that has a lot of reflection going on, a baked texture probably isn't the best choice, so its better to use built-in tools in whatver program you're exporting to.